The production of ethers by the reaction of an isoolefin and an alcohol are well known commercial operations. There are many detailed descriptions of processes for the production of such ethers, in particular, methyl tertiary butyl ether (MTBE) and tertiary amyl methyl ether (TAME). These ethers have long been known as useful octane blending agents for gasoline motor fuels due to their high octane number (ROM) of about 120. More recently ether compounds as gasoline blending components have been highly valued as supplying oxygen to meet reformulated gasoline requirements. Processes for the production of MTBE and TAME by reacting methanol with isobutylene or isoamylene, respectfully, are among the most widely known processes for the production of such ethers.
Processes for the production of such ethers have suffered from a shortage of the necessary isoolefins for reaction with the alcohols to provide products. Feedstreams for etherification processes typically consist of a wide variety of olefinic and paraffinic isomers. It has been known to increase the available feedstock by the dehydrogenation of paraffins and the skeletal isomerization of olefins. Methods for the dehydrogenation of paraffins, in particular isoparaffins, are well known in the art as are processes for the skeletal isomerization of normal olefins to isoolefins.
The use of isomerization to increase the isoolefins available for etherification requires the recycling of the isomerization effluent as feed to the etherification zone. Adding a recycle stream that includes normal alkenes and typically alkanes along with the additional isoalkenes increases the total mass flow rate to the etherification reactor. The higher mass flow to the etherification reactor can require an entirely new etherification reactor train due to inadequate capacity of the existing etherification reactors. In grass roots etherification addition, higher efficiency etherification reaction trains will use two reactors. An increased recycle adds to the cost the expense by increasing the size of two reactors.
An additional problem with etherification flow schemes is that the olefinic and paraffinic isomers of any given carbon number have relatively close boiling points. Separation of the isomers in an efficient manner to enhance the production of ether as well as the conversion of unreacted products to additional reactants has been difficult. Methods for the various separations have included adsorptive separations as well as extractive distillations. There is a need for etherification and isomerization process arrangements that simplify the separation of olefinic and paraffinic isomers to provide products and reactants and reduce the cost of recycling additional reactants for the production of ether.